The aim of the present study was to investigate the effect of ketosis status on milk yield and quality traits of Holstein Friesian cows. Individual milk samples (n =15,674) of first-lactation cows from 5 to 60 days in milk (DIM) were collected during the official monthly test-day milk recording scheme and analysed for milk quality traits using Fourier transform infrared (FTIR) spectroscopy. Also, betahydroxybutyrate (BHB) was predicted by FTIR spectroscopy and used to classify records as normal, suspect or ketotic. Data were analysed with a linear mixed model including ketosis status, DIM and their interaction as fixed effects, and cow, herd-test-day and residual as random effects. Overall, ketotic cows exhibited the worst performance in terms of milk yield and quality compared to suspect and normal cows across the first 60 DIM. Results suggest that elevated milk BHB concentrations have a strong negative effect on milk yield and quality traits in early lactation.